Illumination Theory, though it's fairly close. I'm kind of surprised that people have been so definitive as to say "__ by far".
I absolutely LOVE the main riff in IT, and when it's reprised later in the song and later under the guitar solo, it's a prog-gasm moment.
TCOT certainly has some awesome moments, I really like the intro and the final verse, but as we all know, the lyrics are pretty silly, which hurts it.